1. Field of the Invention
This invention relates to a clamping arrangement for clamping a workpiece to be processed along a processing shaft in a processing machine.
2. Discussion of Related Art
Processing machines, for example, circular grinding machines, milling machines or lathes, are comprised of one or several processing shafts, along which a workpiece clamped in the processing machine can be worked. In this case, the workpiece is clamped in the processing machine by a clamping arrangement. Depending on the processing machine and the work process, the workpiece is either clamped along the processing shaft or radially with respect to the processing shaft.
For example, for clamping along the processing shaft it is known to clamp the workpiece between two cone-shaped or truncated cone-shaped clamping tips, which can be displaced relatively to each other along the processing shaft. The clamping tips can be adjusted in relation to each other using power. In connection with a tube-shaped workpiece, the clamping tips enter the ends of the workpiece, partial under spring pressure. For adapting the clamping tips to different workpieces the clamping tip can be in the form of a clamping head with clamping elements, which are exchangeably arranged on it. In this case, the parallelism is oriented by the axis-parallel displacement of the clamping tips in relation to the processing shaft. Here, the clamping arrangement includes the two clamping tips, as well as the displacement mechanism for pressing the two clamping tips against each other.
A clamping tip, which can be arranged on a tailstock and is supported on a tailstock sleeve, is known from German Patent Reference DE 195 33 456 B4. The clamping tip is in one piece and has a shape of a circular cone.
A co-rotating clamping tip or tailstock sleeve, seated in a housing, and which is also embodied in one piece and has a shape of a circular cone, is known from German Patent Reference DE 36 22 725 A1.
Because of the rigid clamping of the clamping tips in one piece and shaped as circular cones, there is the danger of deforming tube-shaped workpieces, for example, which have centering or clamping faces which are inexactly produced or deformed by hardening distortion while clamping them between the clamping tips. Also, dirt accumulation at the clamping tips or the workpiece, for example, can result in considerable deformation in connection with the described clamping situation.
For radial clamping in relation to the processing shaft, a clamping chuck is customarily employed, which can be rotated around the processing shaft, can be driven and has clamping jaws, which are radially movable, can be adjusted, for example by an adjustable wrench, and can be clamped against the workpiece. In this case, the clamping jaws are such that the workpiece can be clamped between the clamping jaws from the direction of its exterior circumference or, in case of a tube-shaped workpiece, from its interior circumference. In this case the clamping arrangement comprises the clamping chuck, which has a chuck body, radially adjustable clamping jaws, and an adjusting mechanism for the simultaneous radial displacement of the clamping jaws.
Compared with the previously described clamping tips, it is possible to call the clamping chuck body a clamping head and the clamping jaws clamping elements, so that a clamping arrangement, regardless of the clamping situation, comprises a clamping head, clamping elements adjustably arranged on the clamping head, as well as an adjusting mechanism. A clamping head for use in a processing machine customarily has three clamping elements, which center the workpiece between three contact points formed between the clamping elements and the workpiece while clamping.
A clamping arrangement is known from German Patent Reference DE 296 24 215 U1, which has a clamping chuck body with at least two radial jaw guidance elements for a clamping jaw, including a base jaw and a crown jaw which are radially adjustable in the jaw guidance element.
A clamping arrangement is known from German Patent Reference DE 203 20 649 U1, having a clamping chuck body and several clamping jaws, which are movably arranged in radial jaw guidance elements and can be adjusted together radially with respect to the clamping chuck axis by an adjusting mechanism.
Because of the adjusting mechanism causing a rigid displacement of the clamping jaws, a deformation of the workpiece occurs in such clamping arrangements during the clamping process which, following the unclamping of the workpiece after its processing, has a negative effect on the accuracy of its shape and measurements, because in every case the workpiece again assumes its original shape.
A clamping arrangement is known from German Patent Reference DE 199 34 375 A1, which comprises a clamping chuck with two clamping jaws, which can be radially adjusted and clamped against the workpiece. Each of the clamping jaws is arranged pivotable to a limited extent around pivot shafts extending parallel with the processing shaft. Here, the pivotable clamping jaws can be adapted to a limited degree to the circumference of a workpiece by being pivoted around the pivot shafts extending parallel to the processing shaft. However, no adaptation to workpieces of variable shapes in the axial direction along the processing shaft is possible here, so that with this type of clamping a point-like resting of the clamping jaws against the workpiece occurs. Because of this, strong deformations occur in the areas in which the clamping jaws rest point-like against the workpiece, together with a corresponding bad result of the workpiece shape and measurements following unclamping.
A clamping arrangement is known from German Patent Reference DE 36 20 260 A1, which comprises a clamping chuck with radial clamping jaws, which can be clamped against the workpiece. Here, the workpiece is clamped between two clamping tips. The clamping chuck is arranged concentrically in relation to a clamping tip. For being able to compensate eccentricities in the workpiece clamped between the tips, the clamping chuck is arranged freely displaceable with respect to the clamping tip both in the radial and the axial direction. Deformations already occurring when clamping the workpiece between the clamping tips cannot thus be compensated.
Thus, it is disadvantageous in connection with the prior art that, for example with very precise workpieces which are exactly shaped in prior processing stages, in particular with tube-shaped and/or thin-walled workpieces, these are deformed when being clamped, because the clamping elements forcibly impress their shape on the workpiece during clamping, or that the workpiece is deformed corresponding to the positions of the clamping elements, and thus the position of the spot-shaped or line-shaped contact faces between the clamping head and the workpiece. One problem arises in connection with inexactly preshaped workpieces that are substantially centered in accordance with the shape of their exterior or interior circumference in the area of or near the spot-shaped contact faces between the clamping head and the workpiece, and not in accordance with a preferred processing shaft which, for example, is oriented relative to the workpiece to be produced.